Messages in this thread | | | Date | Thu, 22 Apr 1999 13:53:20 +0200 | From | Harald Koenig <> | Subject | Re: RFD: tickadj way too small? |
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On Apr 22, Ulrich Windl wrote:
> Hello, > > I don´t know what the initial reasoning for "500/HZ" was, but I think > the value for tickadj is way too small in the Linux kernels. > > (tickadj limits the speed of a adjtime() system call) > > The current rate is 0.5ms per second. Thus a correction of 128ms > needs 256s, almost 5 minutes. A correction of one second (not unusual > if the computer was powered down for a day) almost needs half an hour.
IMHO 128ms is a pretty huge difference and should almost never happen. and if it happens, waiting 1/2 hour shouldn't be a problem (as it never happens anywy -- per definition;)
and at powerup you first should use ntpdate or similar to step the clock then.
> The current rate of 0.05% (500PPM) is too slow in most cases. Many > systems use much larger values. > > I'm suggesting to boost the value of tickadj by a factor of 100. > Therefore tickadj will be 50000/HZ, 500 for i386. This will result in > a correction of 50ms per second (5%).
NO, that's _WAY_ too large! if you're trying to do some timing/benchmark in this period you'd get 5% error just because of tickadj. IMHO that's completely out of range! waiting a bit longer to get clocks in sync is much preferable than to risk 5% errors in timing/sleep intervals etc.
> (My PPSkits added the ability to adjust the value of tickadj during > runtime, but we need a reasonable default for most cases. BTW: > there´s an additional patch to fix compilation problems on i386 with > PPSkit-0.6.0: PPSkit-0.6.0-add-1.diff.gz, available at the usual > sites since this morning) > > I'm not subscribed to this list, but I'm willing to accept any > contributions regarding this thread. If nobody objects, I'll put a > higher value in the next PPSkit, and finally I'll suggest a patch for > the stable kernel. > > Regards, > Ulrich > P.S.: I'm suggesting to merge PPSkit-0.6 into the upcoming Linux 2.3 > tree. Currently FreeBSD is way ahead in timekeeping (according to Mr > Mills and Mr. Kamp)... > > > - > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.rutgers.edu > Please read the FAQ at http://www.tux.org/lkml/
Harald -- All SCSI disks will from now on ___ _____ be required to send an email notice 0--,| /OOOOOOO\ 24 hours prior to complete hardware failure! <_/ / /OOOOOOOOOOO\ \ \/OOOOOOOOOOOOOOO\ \ OOOOOOOOOOOOOOOOO|// Harald Koenig, \/\/\/\/\/\/\/\/\/ Inst.f.Theoret.Astrophysik // / \\ \ koenig@tat.physik.uni-tuebingen.de ^^^^^ ^^^^^
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